Heretofore, vacuum cleaner-blower units, particularly of the smaller, inexpensive commercial type under 5 horsepower, suitable for portable or semi-portable use by an operator, were a compromise. Either they developed adequate vacuum or pressure (depending upon use as a vacuum cleaner or blower) at the expense of generating considerable noise, to the point of being objectionable to the operator; or they were relatively quiet but developed less than the desired vacuum or pressure.
Anyone who has heard a vacuum cleaner in operation, even of the domestic type, appreciates that the intake and discharge of air from the blower creates considerable noise. It is surprising to discover that nearly half the noise is generated by the electric motor, particularly the cooling air flow for the motor, and that to have a relatively quiet vacuum cleaner-blower assembly the noise generated by both the blower and motor must be reduced.